 Hi, I'm Zor. Welcome to Inizor Education. I would like to continue talking about energy related to chemistry. Today's lecture is about inter-atomic bonds. Now, this lecture is part of the course Physics for Teens, which is presented on unizor.com. If you found this lecture anywhere else, like on YouTube or something like that, I do suggest you to go to the website because it basically contains the reference through the same lecture, but also every lecture is having the textual part, basically it's like a textbook. Plus, there are certain exams and there is a functionality, it's a course actually. On the website it's a course, not just individual lectures. And the course obviously is logically combines the different parts, which are related to each other in certain order. Also, on the same website you can find Math for Teens, which is a prerequisite for this course because there are lots of mathematics in physics, and so that's why I first created the Math for Teens and now this is the Physics for Teens based on the math. Okay, back to chemical energy. Well, by now you know that mechanical energy is related to objects, energy related to heat, thermal energy is related to moving of the molecules inside the objects, so this is the one level down. Now when we are talking about chemical energy we are going deeper into the molecules. We are going to atoms which are combined into the molecules and rearranging these atoms is what chemical reaction actually does and during this rearrangement some energy is either produced or consumed, chemical energy. So, what we are talking about right now is that the molecules contain atoms and somehow the rearrangement of these atoms from one set of molecules to another produces or consumes energy, whereas this energy coming from. Well, and another obvious question is why the atoms are combined into molecules and what actually keeps them in the molecule itself. Well, that's what interatomic bonds actually is all about. So, every molecule which basically is the smallest part of any substance which maintains the properties of this substance contains atoms and these atoms are bonded together into this molecule using the interatomic bonds. So, let's talk about how exactly these interatomic bonds are working, what's the kind of a mechanism behind it. Well, what's very interesting is that there are certain models which people came up with which describe this interatomic bonds and none of these models are exactly what's really happening in the nature. These are all our models. However, experiments basically show that these models both seem to correspond to whatever we observe in the nature. So, we are considering these models as well kind of truthful models to an extent until some experiment will show that well these models are not exactly what's going on. There is something else and then theorists are coming up with maybe a little bit better model which better corresponds to new experiments without obviously breaking the old one. So, the physics behind the structure of the atom is really extremely complex, extremely convoluted and unfortunately there are many theories which contradict each other etc. So, what I will talk about is something relatively simple model which relatively corresponds to a certain degree to what's really happening in the world but again by no means I'm stating that this exactly what's going on in the real world. This is our model which more or less closely represents what's going on. So, I'm talking about orbital model of the atom. Well, one of the first inventors of this model was great physicist from Copenhagen, Nils Bohr. So, he lived in the beginning of 20th century and he was one of the founders of all the contemporary physics. Ok, so let's talk about orbital model of atoms. According to this model and again I'm repeating this is a model. I'm not sure what exactly is going on inside the atoms. So, according to this model the model contains a nucleus and certain number of electrons which are circulating around this nucleus on certain orbits. Now, nucleus in its turn contains certain number of particles, actually two particles, protons and neutrons. Protons carry positive electrical charge, electrons around it carry negative charge and the number of protons and electrons should be the same to keep the atom neutral, electrically neutral. Otherwise it will be very unstable. Neutrons do not have any electrical charge. Now, the size of the atom relative to the size of the nucleus is extremely large. It's like size of the solar system relative to the size of the Sun itself. Sun takes, well, substantial amount of space but no comparison with the size of the entire solar system when all these outer orbits are actually taken into account. However, the mass of the atom is here in a nucleus. Electrons are very, very, very light. I mean, millions of, I don't really remember what exactly is, but we can safely say that the mass of the atom is concentrated in its nucleus. It's a sum of masses of all the protons and neutrons which are more or less the same, almost the same in their mass. So, protons and neutrons are inside, electrons are outside. For our purpose of talking about inter-atomic bonds, we actually have to concentrate on the electrons. Now, here's another important thing. For reasons, well, to tell you the truth, unknown to me. And most likely it's unknown to many other people, I mean professional physicists. So, for these reasons, if this is a nucleus and these are different orbits, on every orbit there is certain maximum number of electrons which can circulate on this particular orbit, not bumping into each other. Because if they bump into each other, they will probably kick whatever the extra electron is to another orbit. So, there is certain number, maximum number of electrons on each orbit. And, as I was saying, for reasons unknown to me, the closest to the nucleus orbit has maximum of two electrons. The next one, 8, the next one, if I'm not mistaken, 14. And let's not go any further than that. So, these are maximum. Now, different elements have different number of electrons. Like, for instance, hydrogen has one electron, carbon has six, oxygen has eight electrons. Now, the electrons are filling up the orbits. Now, the one electron here doesn't even fill the first orbit. So, it's circulating somewhere on the closest to a nucleus orbit. Now, this one, the carbon, well, it has two electrons on the inner orbit and four electrons on the next one. Now, the total number of electrons on the next one is 8. So, it's not filling the second orbit. It completely fills the first one and the second one it does not fill completely. It has only four out of maximum eight. Now, oxygen has eight, which means it has two in the inner orbit and six in the second one. So, there are two spaces left out of eight. It has only six in the second orbit, two in the first, six in the second. Now, this is a key to understand how different atoms are connected to each other. You can imagine this connection as somehow related to the electrons on the outer layer, on the outer orbit of this particular, of any particular atom. For instance, in case of hydrogen, so we know there is only one electron. It can be two, which means it can absorb another electron or share your, it can share its own electron with something else. So, the purpose of any bonding between atoms is to fill up the outer layer. So, this electrostatic kind of a desire to be complete is the source of the bonding. And how can we make complete? For instance, if you have atom of hydrogen just by itself. Well, by itself it's not complete because there is only one electron. However, if you will have two different atoms of hydrogen. Now, this one has one electron and this has one electron. If for some reason they can share these electrons, so these electrons are on both orbits. So, this one may be here, may be here and this one may be here and may be here. So, they're sharing and these two electrons are filling up the orbits in both cases. So, this sharing is one of the different kinds of bonding between the atoms. There are others as well, but we're not going into the depths of different kinds of bonding. I just wanted to share with you that there are certain mechanisms of inter-exchange of these electrons between elements by which they may complete their orbits. So, now if these two electrons are shared between these two atoms and I have no idea how it's done. However, if they are shared and that's what basically contemporary physics are saying. Then, this layer and this layer, the first layer which can hold maximum two, that's complete, will be filled up. Now, on another hand, if you have an element with already two electrons, like helium for instance, helium has two electrons on the first orbit, it's already complete and this is the inert gas. It doesn't really take into any reaction with anything because it has a complete number of electrons on the orbit. However, something like hydrogen, it needs something else to be complete. So, for instance, it can be combined with another atom of hydrogen forming a molecule. So, this is a molecule which we call a molecule of hydrogen and we call it H2 because there are two hydrogen atoms which are sharing each one having a single electron, but these two electrons somehow are sharing the orbits and atoms are stable now, connected through this sharing, the atoms are stable. So, this is a stable gas. Atomic hydrogen is not stable. It will immediately take into reaction with atom and it will form the molecule. Same thing, atomic oxygen. Atomic oxygen is a very reactive kind of substance. It will always look for something to form a molecule, to fill up its own outer layers. Now, what happens with oxygen, by the way? With oxygen, we have eight electrons. Two is filling up the inner structure and we have six on the second one. Out of eight. So, we have two spaces not filled up. So, what happens is if you have this electron and this electron, now you have six spaces, six electrons on the outer orbit. So, these four, one, two, three, four are kind of private and these four are kind of private, but these are shared. So, these pair of electrons, now in this case we have one pair of electrons. In this case, we have two pairs of electrons and they are connected, they are shared between these two atoms and they are making a connection. So, somehow they are shared. So, that's how we have a molecule of oxygen which contains two atoms which share two pairs of electrons. So, that's why we are actually structuring molecule of hydrogen this way and molecule of oxygen this way. Number of these bars indicate number of pairs of electrons they are sharing. Well, this seems to be a stronger connection, right? Because there are two links and this is one link. Now, does it mean that oxygen always has to have double link with something else? Not necessarily because it can connect to some other things in a different configuration and we will go into this. So, my next configuration is carbon related to hydrogen somehow. So, we are talking about gas called methane. Now, it's a CH4. Now, let me just put structure. H, C, H, H, H. What does it mean? Okay, C has six electrons, two on the inner orbit and four on the next one out of eight. So, we have four spaces to be completed somehow. So, this has four which are needed to fill it up. These all have one single one on their orbit. So, if these guys are sharing these electrons with this one, everybody is complete, right? So, we have these four electrons are shared with these four electrons making the orbit of each H a pair and making the orbit of carbon, the outer orbit, equal to eight. So, that's what's happening in this case. And this is the structural formula. C connected with a single link to four different Hs. One single atom of carbon with four different atoms of hydrogen. Next example. Next example is carbon dioxide, CO2. We all know about this gas. We are breathing in the oxygen and we are breathing out carbon dioxide, right? Now, how is this arranged? Well, let's just think about it again. Oxygen having eight minus two on the inner, six on the outer. So, it's two extra which needed to complete. C has two on the inner, four on the outer. So, what happens is this following. That's the structure of the carbon dioxide. So, C has four electrons on the outer orbit. Oxygen has six ones. So, two and two and two private. Two and two and two private. These guys are shared. These guys are shared. Now, carbon has eight. One, two, one, two. One, two, one, two. It has eight on outer orbit because these are shared electrons. And each oxygen has eight. This one and this one. All right? So, that's how we have CO2. Carbon dioxide. Next, a little bit more complex, but for the purpose. The ethanol. Now, ethanol has the formula C2H6. Well, sometimes they are doing it like CH3. CH2OH. Whatever it is. Anyway, this is a representation of the structure of ethanol. And here is the structure. So, we have two atoms of carbon connected to each other. Now, these guys are connected to hydrogen. And this one is connected to hydrogen through the molecule of oxygen. Again, think about, we need two extra for oxygen, remember this? We need four extra of four carbon and we need one extra for H. So, if you will pay attention to this picture. So, every link represents one shared electron. Between this and this. Between this and this. So, for all, we have two extra shared electrons which will complete its outer layer. For each C, we have four, you see? This four and this four. We have four shared electrons to complete its outer layer, which has four, but needs eight. And obviously, each hydrogen needs one more, so we have this. What's very important, why I actually wanted to put this. Remember, back the CO2 has this connection. So, between C and O, between carbon and oxygen, we have double link here, because it's a double pair, two pairs of electrons connected. Here between carbon and oxygen, we have one. So, it's not the atoms by themselves which determine the link. It's the whole structure of the molecule. The same two different atoms can be connected using one pair of electrons in one case and two pairs of electrons in another case. So, this is double bond. This is single bond. This is CO and this is CO. So, there are different bonds between even the same atoms. And whenever we are calculating energy or whatever is necessary to break the bond, and that's what chemical reaction is. It's breaking some bonds and creating other bonds. So, we have to really compare. So, whenever we do this, we have to calculate not only based on what kind of atoms are inside the molecules, but the structure of the molecules and what kind of bonds are between the molecules. So, that's why I wanted to present you the molecule of ethanol as different connection between the same carbon and oxygen than, let's say, in carbon dioxide. And what else? And my last example is hydrogen peroxide. It's not exactly water. Remember, water is H2O. Well, H2O basically means this. Now, hydrogen peroxide is this one. Now, how is this connected? Well, this is how. HOOH. So, again, in some cases, O and O are connected as in oxygen gas with a double link. But in case of hydrogen peroxide, the connection is single link here because another link is used to connect to H to hydrogen. All right. So, again, the purpose of this lecture was to explain that there are interatomic bonds, which are, well, you can say these are the forces actually, which keep the molecule together. Now, in certain cases, these forces might not actually be very stable. But like in case of hydrogen peroxide, it basically converts into regular water releasing some extra oxygen. But in most cases, molecules are stable. And they're stable because these bonds between different atoms are keeping the molecule together. Now, we were talking about one particular kind of bond. It's the sharing of electrons. There are some others. There are some metallic bonds and there are some others, actually, ionic bonds. I don't want actually to go into the depths of this. My purpose was not really to talk about what kind of bonds exist, but just to make sure that you understand that we need interatomic bonds. And interatomic bonds can actually be different, like single, double, can be triple. If you need three different pairs of electrons to share or something else. So they may be different and it's not the atoms per se that determine the bond. It's the whole molecular structure determines what kind of a bond exists between the atoms. And in the next lecture, whenever we will start calculating the energy of consumed or released by the chemical reaction, we will calculate this energy based on what kind of a bond this is. Is it a single bond between carbogen and oxygen or is it a double bond or whatever else it is? Well, that's basically enough for general understanding how the molecules are built from the atoms. I did mention this before, but I think it's quite really amazing that you have so many different molecules, like thousands, millions of different molecules, different substances, obviously. Now, all these molecules are built from about a hundred different types of atoms, which are classified in the periodic table of man to live. And each atom contains basically, well, three major elementary particles, proton, neutrons and electrons. And again, they're just combined into different quantities to make different atoms. So the atom of carbon contains exactly the same protons and neutrons and electrons as atom of oxygen just in different quantities and you have a different atom. So the millions of molecules are built from about a hundred different atoms and these hundred atoms are built basically from three major particles. So that's how the world is built according to our model, how it is in the reality. Nobody knows. Anyway, that's it for today. Thank you very much and good luck.